As for the oxide superconductor, a critical temperature (Tc) is high compared with a conventional alloy system superconductor such as Nb3Sn system, and applied equipments such as electric power cable, transformer, motor, and electric power storage system can be operated under the liquid nitrogen temperature. Therefore, the making of the wire rod is studied energetically. Especially, in ReBa2Cu3O7-y (RE shows at least more than one kind of element selected from Y, Nd, Sm, Gd, Eu, Yb, Pr or Ho, and hereinafter called ReBCO) superconductor, because the reduction of the conducting current is small in the high magnetic field area, that is, because the magnetic-field property in the liquid nitrogen temperature is excellent compared with Bi system superconductor, the practical high critical current density (Jc) can be maintained. And, in addition to the excellent property in the high temperature area, because the manufacturing method which does not use silver of the precious metal is possible and the liquid nitrogen can be used as the refrigerant, the cooling efficiency improves remarkably. Therefore, it is extremely advantageous economically and the making of the wire rod is expected as the next-generation superconducting material.
Generally, the Re system oxide superconducting wire rod has the structure that at least one layer or plural layers of the biaxially-oriented oxide layer is formed onto the metal substrate, and the oxide superconducting layer is formed onto it, and further, the stabilizing layer which undertakes the role as the surface protection of the superconducting layer, the improvement of the electric contact, and the protection circuit in the excessive energization is stacked. In this case, it is known that the critical current property of the ReBCO wire rod depends on the in-plane orientation of the superconducting layer, and is influenced greatly by the intermediate layer which becomes the basic material, and the in-plane orientation and the smooth surface property of the oriented metal substrate.
The crystal system of the ReBCO superconductor is the rhombic crystal, and because the lengths of three sides of x axis, y axis and z axis are different and the angles among the three sides of the unit cell are also slightly different respectively, it is easy to form the twin crystal And because the slight gap of the azimuth generates the twin crystal grain boundary and reduces the conducting property, to bring out the property of the material in the conducting property, in addition to aligning of the CuO surface of the inside of the crystal, the aligning of the crystal orientation in the in-plane also is demanded. Therefore, the making of the wire rod has the difficulty compared with the Bi system oxide superconductor.
The manufacturing method of the making of the wire rod which improves the in-plane orientation of the crystal of the ReBCO superconductor and aligns the azimuth direction in the in-plane is same as the manufacturing method of the thin film. That is, the in-plane orientation and the azimuth direction of the crystal of the ReBCO superconducting layer is improved by forming the intermediate layer whose in-plane orientation and azimuth direction were improved onto the tape-shaped metal substrate and by using the crystal lattice of this intermediate layer as the template.
The ReBCO superconductor is studied in various manufacturing processes now, and various biaxially-oriented metal substrates which form the in-plane oriented intermediate layer onto the tape-shaped metal substrate are known.
Among these, at present, the process that the highest critical current property is shown is a method of using the MAD (Ion Beam Assisted Deposition) substrate. In this method, onto the polycrystalline high strength and non-magnetic tape-shaped Ni system substrate (hastelloy etc.), the particle generated from the target while irradiating the ion from a direction of the constant angle to the normal line of this Ni system substrate is deposited by pulsed laser deposition (PLO). And, the intermediate layer (CeO2, Y2O3, YSZ etc.) or the intermediate layer of the double-layered structure (YSZ or Rx2Zr2O7/CeO2 or Y2O3 etc.: Rx shows Y, Nd, Sm, Gd, Ei, Yb, Ho, Tm, Dy, Ce, La or Er) which has the fine grain size and the high orientation and inhibits the reaction with the element which comprises the superconductor is formed. And, after forming the CeO2 film onto it PLD method, YBa2Cu3O7-y (hereinafter called YBCO) layer is formed by PLD method or CVD method, and the superconducting wire rod is formed (for example, refer to Patent document No. 1 to No. 3).
However, in this process, because all intermediate layers are formed by the vacuum process in the gas phase method, although this process has the advantage that the dense and smooth intermediate layer film can be obtained, there are problems that the production speed is slow and the production cost rises. Although the processes of forming films by using sane gas phases other than this IBAD method have been studied, the effective means which solve the problems of the production speed and the production cost have not been reported.
The most effective process for attaining the low cost is the MOD process where the organic acid salt or the organic metallic compound is used as the raw material, and the oxide layer is formed by giving the thermal decomposition and the crystallization heat-treatment after coating this solution onto the surface of the substrate. Although this process is simple, because the long time heat-treatment in high temperature is necessary, according to the generation of cracks originating from the contraction in volume of film at the thermal decomposition, the non-uniform reaction by the imperfect of grain growth, and the decrease of the crystalline by such as the diffusion through the crystal grain boundary of the metallic element which constitutes the substrate, it was difficult to obtain the film having the function enough as the intermediate layer.
Generally, as the intermediate layer of the superconductor, although CeO2 which is formed by PVD method is used as described above, because CeO2 intermediate layer is excellent in the lattice consistency with the YBCO layer and in the oxidation resistance, and because the reactive property with the YBCO layer is small, this depends on what is known as one of the most excellent intermediate layer. When this CeO2 intermediate layer is formed by MOD method, the cracks are generated depending on the large difference of the coefficient of thermal expansion with the metal of the substrate, and it becomes impossible to accomplish the function as the intermediate layer. Although the generation of cracks is inhibited when the film is formed using the solid solution that Gd is added to CeO2 onto the Ni substrate by MOD method, because the diffusion of the element from Ni or Ni alloy substrate cannot be stopped in the inside of the intermediate layer, there was a problem that the superconducting property decreases. In order to prevent the diffusion of the element which constitutes this substrate, the study of the intermediate layer material that Gd is substituted to Zr is performed. The effect of preventing the diffusion is admitted, and the property of Jc>1 MA/cm2 is obtained.
On the other hand, as the composite substrate which is excellent in the mechanical strength and the orientation, the following oriented substrate for film formation is known. That is, the non-oriented and non-magnetic first metal layer and the second metal layer which is pasted onto the first metal layer and has the texture whose surface layer at least is oriented are provided. And the first metal layer has the higher strength than the second metal layer. And this substrate has the high strength while maintaining the good orientation (for example, refer to Patent document No. 4).    Patent document No. 1: Japanese Patent Publication No. Hei04-329867    Patent document No. 2: Japanese Patent Publication No. Hei04-331795    Patent document No. 3: Japanese Patent Publication No. 2002-203439    Patent document No. 4: Japanese Patent Publication No. 2006-127847